Micro-pits Array Research Articles

Electrochemical Machining of Micro-Pit Arrays on a GH4169 Alloy with a Roll-Print Mask Using a C6H5Na3O7-Containing NaNO3 Mixed Electrolyte.

GH4169 alloy, a nickel-based superalloy known for its excellent high temperature resistance, corrosion resistance, mechanical properties, and high-temperature tribological properties, is widely used in industrial applications, such as in gas turbines for space shuttles and rocket engines. This study addresses the issue of electrolyte product residue in the electrochemical machining process of a GH4169 alloy by utilizing a C6H5Na3O7-containing NaNO3 new mixed electrolyte. Comparative investigations of the electrochemical behavior and electrolyte product removal mechanisms at different concentrations of C6H5Na3O7 additive in NaNO3 solutions were conducted. The effects of additives, applied voltage, and the rotating speed of the cathode tool on the processing performance of micro-pit arrays on a GH4169 alloy were analyzed. The results indicate that the mixed solution containing C6H5Na3O7 significantly improves the localization and geometric morphology of the micro-pits compared to a single NaNO3 solution. The optimal electrochemical machining parameters were identified as 0.5 wt% C6H5Na3O7 + 10 wt% NaNO3 mixed electrolyte, 12 V applied voltage, and 0.1 r/min rotating speed of the cathode tool. Under these conditions, high-quality micro-pit arrays with an average diameter of 405.85 μm, an average depth of 87.5 μm, and an etch factor (EF) of 1.67 were successfully fabricated, exhibiting excellent morphology, localization, and consistency.

Effect of the Surface Peak-Valley Features on Droplet Impact Dynamics under Leidenfrost Temperature.

This study explores the kinetic behavior of droplets impacting microtextured surfaces under a Leidenfrost temperature, employing high-speed photography and picosecond laser micromachining techniques. The investigation focuses on two types of microtextured surfaces with totally different surface peak-valley features: a negatively skewed surface with micropit arrays (Ssk < 0) and a positively skewed surface with micropillar arrays (Ssk > 0). The results indicate that both microtextured surfaces contribute to a higher Leidenfrost temperature compared with the original smooth surface, which is consistent with previous studies. However, it is worth noting that the Leidenfrost points of the micropit and micropillar surfaces showed opposite trends with the microtexture area occupancy. Specifically, the Leidenfrost temperature on micropit surfaces increases with greater micropit area occupancy, while it decreases on micropillar surfaces under similar conditions, which is mainly attributed to the differential impact of area occupancy on droplet heat transfer efficiency. When the microtexture area occupancy is 50%, it is worth noting that the micropit and micropillar surfaces have nearly same roughness (Sa), but the Leidenfrost temperature was notably higher on the micropit surface with negative skewness (Ssk < 0), which was related to differences in vapor flow dynamics. We further find that the Weber number (We) significantly influences the Leidenfrost point, with the droplet impact wall behavior going through the states of film bounce back, ejecting tiny droplets and bounce back, and ultimately droplet breakup as the We increases. The dynamic Leidenfrost point was found to be generally higher than the static point and increases with the We. Finally, we compare the cooling efficiency of these surfaces, and it is found that the micropit surfaces with a negative skewness exhibit superior heat dissipation performance under the same conditions, which proved that the negatively skewed surface may have great potential in high-density heat dissipation technology.

Electrochemical machining process for micropit arrays using a rolling device with a linear cathode and a soft mask

Electrochemical machining process for micropit arrays using a rolling device with a linear cathode and a soft mask

A Bioinspired Surface with Synergistic Effect of Anisotropy and Gradient Microstructures for Controllable Fluid Transportation

The fluid on micro-nanostructures with anisotropy or gradient can exhibit highly inducible wettability that can be found in both nature and artificiality. In this study, inspired by the anisotropic and gradient micro-nanostructures on rice leaf and cactus spine, respectively, we fabricated a wedgy polydimethylsiloxane with ordered micropit arrays (WPOMA) by a rapid strategy to strengthen the property of directional water transportation as a result of their synergistic effect. The unit structure in the array exhibits anisotropy under stretched stress, whereas the unit structure in the long range along the WPOMA shows an arrangement of gradient. Therein, the anisotropic elliptical micropit arrays generated by stretched stress contribute to the axial flow, whereas the gradual change of micropit arrays with morphology gradient contributes to the directional flow. The concurrent axial and directional flows have a great performance in fluid transportation and collection. Additionally, the anisotropic and gradient synergistic micro-nanostructures can be controlled in real time by reversible mechanical stress, which was revealed at the stretched state and hidden at the released state. Meanwhile, the flexible texture effectuated the flow-induced capacity even at the bending state. On the basis of the synergistic effect and switchable wettability, the flexible material paves a way in the potential applications in anti-drag wearable devices, droplet manipulators, and controllable fluid transportation.

Adhesion and machining performance of PVD AlCrN coatings with an ion beam/laser textured substrate

The insufficient adhesive strength of Physical Vapor Deposition (PVD) coatings is still the key issue that needs to be solved urgently for high-efficiency and high-quality difficult-to-machine materials cutting processing. Currently, laser micromachining is extensively utilized to fabricate micro-textures on the substrate to enhance coatings adhesion. However, laser ablation will cause irregular protrusions inside and on the edges of the textures, which could influence the quality of deposited coatings. Therefore, micro-textures were fabricated on the substrate by an ion beam (IBE)/laser machining method, and the influence of IBE/laser textures on the adhesive strength of PVD coatings is revealed. Firstly, a micro-pits array was prepared on WC/Co substrates with different machining parameters, such as laser repetition frequency and ion beam etching time. The micro-topography and mechanical properties of the substrates with different pretreatments were studied. Then, cathode arc-evaporation technique was utilized to deposit AlCrN film on the IBE/laser textured substrates. The scratch test and dry machining experiments of AISI 316 L stainless steel were performed to evaluate the adhesive strength and machining performance of the coated samples with various pretreated substrates. The results demonstrate that laser texturing and ion beam etching both enhanced the coatings adhesion. Therefore, the critical load of the coatings deposited on the IBE/laser textured substrates with 25 kHz laser repetition frequency and 150 min etching time (F N, C2 = 3.39 N) exhibited the highest value, which was 19.4% higher than that of the conventional AlCrN samples (F N, C2 = 2.84 N). Moreover, the cutting forces F X , F Y , F Z and the friction coefficient of IBE/laser textured coated tool were decreased by 18.7%, 20.6%, 10.2% and 16.7% compared with that of conventional coated tool at the high cutting speed of 200 m/min. Finally, the possible mechanisms of IBE/laser texturing pretreatment on enhancing PVD coatings adhesion were discussed. • A micro-pits array is fabricated by an ion beam (IBE)/laser machining method. • Effect of ion beam (IBE)/laser textures on adhesion of PVD coatings is studied. • Mechanism of IBE/laser texturing to improve coatings adhesion is revealed.

High-Content Label-Free Single-Cell Analysis with a Microfluidic Device Using Programmable Scanning Electrochemical Microscopy.

The cellular heterogeneity and plasticity are often overlooked due to the averaged bulk assay in conventional methods. Optical imaging-based single-cell analysis usually requires specific labeling of target molecules inside or on the surface of the cell membrane, interfering with the physiological homeostasis of the cell. Scanning electrochemical microscopy (SECM), as an alternative approach, enables label-free imaging of single cells, which still confronts the challenge that the long-time scanning process is not feasible for large-scale analysis at the single-cell level. Herein, we developed a methodology combining a programmable SECM (P-SECM) with an addressable microwell array, which dramatically shortened the time consumption for the topography detection of the micropits array occupied by the polystyrene beads as well as the evaluation of alkaline phosphatase (ALP) activity of the 82 single cells compared with the traditional SECM imaging. This new arithmetic was based on the line scanning approach, enabling analysis of over 900 microwells within 1.2 h, which is 10 times faster than conventional SECM imaging. By implementing this configuration with the dual-mediator-based voltage-switching (VSM) mode, we investigated the activity of ALP, a promising marker for cancer stem cells, in hundreds of tumor and stromal cells on a single microwell device. The results discovered that not only a higher ALP activity is presented in cancer cells but also the heterogeneous distribution of kinetic constant (kf value) of ALP activity can be obtained at the single-cell level. By directly relating large numbers of addressed cells on the scalable microfluidic device to the deterministic routing of the above SECM tip, our platform holds potential as a high-content screening tool for label-free single-cell analysis.

Shape-Controlled Hierarchical Flowerlike Au Nanostructure Microarrays by Electrochemical Growth for Surface-Enhanced Raman Spectroscopy Application.

How to fabricate Au nanostructures conveniently on microstructured/nanostructured arrays surface with low cost has become a crucial and urgent challenge. In this study, we demonstrate hierarchical flowerlike Au nanostructures with rich nanothorns (HF-AuNTs) through one-step electrochemical deposition. The morphology of the HF-AuNTs is easily manipulated by controlling the applied potential or precursor solution concentration of electrodeposition. The as-prepared HF-AuNTs possessing unique local morphology of thin petals and dense thorns are further applied in the Si micropit arrays to acquire HF-AuNTs microarrays. As an initial detection, these HF-AuNTs microarrays exhibit a fascinating surface-enhanced Raman spectroscopy consistency (relative standard deviation is 7.17%) and sensitivity with the limitation of crystal violet reaching to 10-10 M, and Rhodamine 6G reaching to 10-11 M. The HF-AuNTs microarrays with well-defined shape and elaborate structure may be applicated in SERS substrates, superhydrophobic materials, and so on.

Systematic Analysis of Different Cell Spheroids with a Microfluidic Device Using Scanning Electrochemical Microscopy and Gene Expression Profiling.

The 3D cell spheroid is an emerging tool that allows better recapitulating of in vivo scenarios with multiple factors such as tissue-like morphology and membrane protein expression that intimately coordinates with enzyme activity, thus providing a psychological environment for tumorigenesis study. For analyzing different spheroids, conventional optical imaging may be hampered by the need for fluorescent labeling, which could cause toxicity side effects. As an alternative approach, scanning electrochemical microscopy (SECM) enables label-free imaging. However, SECM for cell spheroid imaging is currently suffering from incapability of systematically analyzing the cell aggregates from spheroid generation, electrochemical signal gaining, and the gene expression on different individual cell spheroids. Herein, we developed a top-removable microfluidic device for cell aggregate yielding and SECM imaging methodology to analyze heterotypic 3D cell spheroids on a single device. This technique allows not only on-chip culturing of cell aggregates but also SECM imaging of the spheroids after opening the chip and subsequent qPCR assay of corresponding clusters. Through employment of the micropit arrays (85 × 4) with a top withdrawable microfluidic layer, uniformly sized breast tumor cell and fibroblast spheroids can be simultaneously produced on a single device. By leveraging voltage-switching mode SECM at different potentials of dual mediators, we evaluated alkaline phosphatase without disturbance of substrate morphology for distinguishing the tumor aggregates from stroma. Moreover, this method also enables gene expression profiling on individual tumor or stromal spheroids. Therefore, this new strategy can seamlessly bridge SECM measurements and molecular biological analysis.

Picosecond Laser Surface Texturing of a Stavax Steel Substrate for Wettability Control

Abstract In this investigation, a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate, which is a key material for mold fabrication in the manufacturing of various polymer products. Three main types of surface textures were fabricated on a Stavax steel substrate: periodic ripples, a two-scale hierarchical two-dimensional array of micro-bumps, and a micro-pits array with nano-ripples. The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air. The results clearly show that this super-hydrophobicity is mainly due to the surface textures. The ultrafast laser-induced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy. The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process. The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to super-hydrophobicity. This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.

Investigation of the influence of ultrasonic stirring on mass transfer in the through-mask electrochemical micromachining process

Surface texturing is a widely accepted approach for friction reduction between mechanical components. Through-mask electrochemical micromachining is a simple and reliable process for metal surface texturing in which mass transport conditions have profound influence on final machined quality. An ultrasonic stirrer is usually adopted for mass transfer enhancement. However, understanding of the effects of ultrasonic stirring on mass transfer is limited, and is far from sufficient for developing guidelines for its practical application. In this work, the influences of ultrasonic stirring parameters on mass transfer have been investigated numerically and experimentally. With the numerical method, periodic pressure change in the electrolyte over time has been obtained, showing that ultrasonic stirring results in drastic transient pressure change in electrolyte fluid fields. Parameters related to ultrasonic frequency, vibration amplitude, and the depth of anode surface immersed in the electrolyte solution influence pressure amplitude. Validation experiments have been conducted and etched surface profile and morphology characterized, which show that the experimental observations are in agreement with numerical predictions. With the optimized mass transfer, well-defined micro-pits array of 30 μm and a smooth etched surface on tin-bronze substrate in large scale have been demonstrated.

Enhanced tensile plasticity of Zr based bulk metallic glasses by a stress induced large scale flow

Tensile plasticity in a Zr-based bulk metallic glasses is achieved through a stress induced large-scale flow. The large-scale flow is activated in a complex stress field which is produced by introducing micro-pits array on specimen surfaces using a laser engraving technique. A flame-like fracture morphology with bigger size (about 10 μm in height) is observed on the fracture surface of specimen, indicating that the size of flow here is far beyond the size of that induced by shear bands. Theoretical analysis accompanied with finite elements modeling (FEM) reveal that the form of high shear zones agrees well with that of the large-scale flow, suggesting that the flow form is changed by the complex stress field. After a comprehensive analyze, the intense shear and suppressing shear bands are concluded to be the two necessary conditions for the stress induced large scale flow.

Femtosecond laser fabricated micro/nano interface structures toward enhanced bonding strength and heat transfer capability of W/Cu joining

W/Cu joining is key for the fabrication of plasma facing components for fusion reactors, which however is very challenging due to the immiscible nature of Cu-W binary system and the mismatch of thermal expansion coefficient between W and Cu. In this research, we proposed a method for comprehensive enhancement of the bonding strength and heat transfer capability of W/Cu joining based on femtosecond (fs) laser fabricated micro/nano interface structures. Four kinds of surface structures, namely pristine structure, nano ripples, micro-cubes array and micro-pits array were designed and fabricated on W by fs laser ablation, which were then introduced into W/Cu interfaces by hot pressing joining at 1000°C, 80MPa. The micro/nano interface structures lead to significant enhancement of W/Cu bonding strength, which reaches 101.58MPa for W/Cu direct joining and 120.43MPa for W/Cu joining with Cu interlayer, increased by about 150% and 190% compared with W/Cu joining with a flat interface. The thermal diffusivity and thermal stress resistance of W/Cu joining are also improved. The strengthening mechanism is recognized to be the combined effects of micro/nano interface structures related interdiffusion between W and Cu and increased resistance against W/Cu interfacial debonding. Our research provides a method for enhanced joining between W and Cu, as well as a vast range of dissimilar materials.

INVESTIGATION OF MICRO-PITS FORMATION ON BILLET SURFACES IN PLANE STRAIN EXTRUSION

Extrusion is a process of pushing a material through a die to yield a desired cross-section product. The application of surface texture has become well known for enhancing tribological performance. In this research, the effect of micro-pits embedded on a work piece lubricated with vegetable oil using plain strain extrusion were studied and compared with those seen with mineral-based oil lubricant. The experiments were conducted at room temperature (around 27℃). A taper die with a 60 die half-angle, with micro-pits array, was prepared. Test lubricants used were paraffinic mineral oil (PMO) VG460 and VG95 and refined, bleached and deodorized (RBD) palm stearin. The results were analysed to determine the extrusion load and the billet’s surface roughness and plastic deformation. RBD palm stearin was recorded as having the highest extrusion load (83.15 kN).

Technique Influence on Cast-Iron Surface Textures Induced by LST

The influence of various technological parameters on laser-textured cast-iron surface is presented in this paper. A kind of micro-pits array was analyzed using single-factor method, where Nd3+: YAG solid laser is applied to obtained regular surface textures, and 3D surface morphology profiler used to compare the surface topographies related to technology. Among of the set of parameters, the distance between working surface and cavity mirror, pumping current and number of pulses were concerned variables in the process of manufacturing of microstructures. The geometry structures for variables were characterized by the radius and depth of micro-pits. Moreover, surface roughness for different technological parameter were expressed with Ra, Rq and Rt. Abbott curve was adopted for valuing the abrasion resistance of given textured surfaces. One optical range of parameters is achieved for improving the level of laser texturing surface.

High-resolution imaging of the immunological synapse and T-cell receptor microclustering through microfabricated substrates

T-cell activation via antigen presentation is associated with the formation of a macromolecular membrane assembly termed the immunological synapse (IS). The genesis of the IS and the onset of juxtacrine signalling is characterized by the formation of cell membrane microclusters and the organization of such into segregated microdomains. A central zone rich in T-cell receptor (TCR)-major histocompatibility complex microclusters termed the central supramolecular activation cluster (cSMAC) forms the bullseye of this structure, while the cellular interface surrounding the cSMAC is characterized by regions enriched in adhesion and co-stimulatory molecules. In vitro, the study of dynamic TCR microcluster coalescence and IS genesis in T-cell populations is hampered by cell migration within the culture system and resolution constraints resulting from lateral cell-cell contact. Here, we detail a novel system describing the fabrication of micropit arrays designed to sequester single T-cell-antigen presenting cell (APC) conjugates and promote IS formation in the horizontal imaging plane for high-resolution studies of microcluster dynamics. We subsequently use this system to describe the formation of the cSMAC in T-cell populations and to investigate the morphology of the interfacial APC membrane.

Copper nanowires and silver micropit arrays from the electrochemical treatment of a directionally solidified silver–copper eutectic

The method of fabricating metallic nanowires from directionally solidified eutectics was applied to the silver–copper system. The silver–copper alloy, 39.9 at.% copper, was directionally solidified in a Bridgman-type oven held at 850 °C. SEM imaging revealed a mixed fibrous and lamellar microstructure. The fastest solidification rates produced fibres and lamellae with widths as small as 300 nm. Electrochemical conditions for the selective dissolution of silver and of copper were determined from the combined Pourbaix diagram for silver and copper and applied to the directionally solidified alloy. Subsequent microscopic investigations yielded copper nanowires with diameters in the 300–640 nm range and hexagonal arrays of micropits in the silver matrix with diameters of 1 μm. The chosen volume fraction of the Ag–Cu system is the only one that matches exactly the theoretical value of π −1 which separates fibrous from lamellar structures. It is demonstrated that the simultaneous formation of fibres and lamellae in the same sample occurs for this unique borderline system.

Optical quality micromachining of glass with focused laser-produced metal plasma etching in the atmosphere.

Recent results are reported about the optical quality surface finish obtained on glass substrates with focused laser beam produced metal plasma etching in the atmosphere. The bombardment of high-speed, high-temperature electrons from an underdense plasma on the surface of glass substrates appears to play a dominant role in this process. The effective laser fluence window for this high-quality glass machining on common microscope slides is relatively narrow. With a Corning microslide 2947, and by use of carbon steel as the plasma source, we obtained parameters between 3.5 and 4.5 J/cm2. Above the upper limit, laser-induced optical breakdown occurs in the glass material and leads to the formation of microcracks. Below the lower limit, the process was found to be ineffective. In these experiments highly defined, clean, sharp-edged, 50 x 50 micropit arrays of 15.0-microm diameter with a depth of 3.2 microm and a center-to-center separation of 18.0 microm were fabricated on Corning microslide 2947 glass substrates.